The present invention relates to a positioning method, a positioning device, and an electronic instrument.
The global positioning system (GPS) has been widely known as a positioning system that utilizes a satellite. The GPS has been utilized for a positioning device provided in a portable telephone, a car navigation system, or the like. A GPS terminal locates its current position by calculating four parameters (i.e., three-dimensional coordinate value which indicates the position of the terminal and a clock error) based on information such as the positions of a plurality of GPS satellites and the pseudo-range between each GPS satellite and the terminal (i.e., positioning calculations).
A GPS satellite signal affected by a multipath may be included in the GPS satellite signals acquired by the GPS receiver. The current position may not be calculated (located) accurately when using a GPS satellite signal affected by a multipath. Specifically, it is necessary to perform positioning calculations while excluding a GPS satellite signal affected by a multipath from the acquired GPS satellite signals. As a method that determines a GPS satellite signal affected by a multipath, a method using an a priori residual (APR) has been known (see JP-A-2003-240836, for example).
In an open-sky environment, the positioning accuracy is generally improved by increasing the number of satellites used for positioning calculations. However, when a building or the like exists in a low elevation angle range with respect to the position to be located, the building may hinder a signal transmitted from a GPS satellite that exists in the direction of the building so that the signal may be affected by a multipath even in the open-sky environment. When performing positioning calculations while increasing the number of satellites, the located position calculated by the positioning calculations may differ to a large extent from the actual position when a signal affected by a multipath is included. This causes the positioning accuracy to deteriorate, whereby a positioning result with low reliability is obtained.